Zeolites are crystalline aluminosilicate compositions which are microporous and which are formed from corner sharing AlO2 and SiO2 tetrahedra. Numerous zeolites, both naturally occurring and synthetically prepared, are used in various industrial processes. Synthetic zeolites are prepared, via hydrothermal synthesis employing suitable sources of Si and Al, as well as structure directing agents such as alkali metals, alkaline earth metals, amines, or organoammonium cations. The structure directing agents reside in the pores of the zeolite and are largely responsible for the particular structure that is ultimately formed. These species balance the framework charge associated with aluminum and can also serve as space fillers. Zeolites are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent zeolite crystal structure. Zeolites can be used as catalysts for hydrocarbon conversions, which can take place on outside surfaces as well as on internal surfaces within the pore.
In U.S. Pat. No. 6,756,030 B1, a new family of materials designated UZM-8 is disclosed. The UZM-8 materials are zeolitic aluminosilicates ranging in Si/Al ratio from 6.5 to 35. They are prepared from reaction mixtures employing organoammonium structure directing agents with preferred examples being diethyldimethylammonium (DEDMA), ethyltrimethylammonium (ETMA), and hexamethonium (HM) cations and optionally alkali or alkaline earth metals and/or other organoammonium cations. The UZM-8 materials have a unique x-ray diffraction pattern and a composition on an as synthesized and anhydrous basis expressed by an empirical formula of:Mmn+Rrp+Al1−xExSiyOz where M is at least one exchangeable cation selected from the group consisting of alkali and alkaline earth metals, “m” is the mole ratio of M to (Al+E) and varies from 0 to about 2.0, R is at least one organoammonium cation selected from the group consisting of quaternary ammonium cations, diquaternary ammonium, protonated amines, protonated diamines, protonated alkanolamines and quaternized alkanolammonium, “r” is the mole ratio of R to (Al+E) and has a value of about 0.05 to about 5.0, “n” is the weighted average valence of M and has a value of about 1 to about 2, “p” is the weighted average valence of R and has a value of about 1 to about 2, E is an element selected from the group consisting of gallium, iron, boron, chromium, indium and mixtures thereof, “x” is the mole fraction of E and has a value from 0 to about 1.0, “y” is the mole ratio of Si to (Al+E) and varies from about 6.5 to about 35 and “z” is the mole ratio of O to (Al+E) and has a value determined by the equation:z=(m·n+r·p+3+4·y)/2.
Applicants have now modified these UZM-8 materials in order to change some of their properties. By using one or more techniques selected from acid extraction, calcination, steaming and ammonium hexafluorosilicate treatment, applicants have been able to control the aluminum content of the UZM-8 zeolites to nearly all silica while maintaining their structure and porosity. Dealumination strategies are known in the art and are given by Breck (see D. W. Breck, Zeolite Molecular Sieves, Wiley and Sons, New York, (1974), p. 441) and Skeels and Breck (see U.S. Pat. No. 4,610,856). The result is a modified UZM-8 (UZM-8HS) material containing less aluminum than the starting UZM-8 composition. Control of the Al content in the zeolite allows one to tune the properties associated with the Al, such as ion-exchange capacity and acidity thereby providing improved catalysts and/or adsorbents. This new family of materials is designated UZM-8HS.
Because of the changes in the UZM-8HS compositions, they have been found to be useful in various hydrocarbon conversion processes such as isomerization of alkyl aromatic compounds, alkylation of aromatic compounds, etc.